The invention relates generally to the field of inhalation drug therapy, and in particular to the inhalation of aerosolized chemical substances. In one aspect, the invention provides a portable inhaler having a cartridge for storing a chemical substance in a dry state and a liquid dispenser to introduce a liquid to the substance to form a solution. Immediately after formation of the solution, the inhaler aerosolizes the solution so that it may be administered to a patient.
The atomization of liquid medicaments is becoming a promising way to effectively deliver many medicaments to a patient. In particular there is a potential for pulmonary delivery of protein peptides and other biological entities. Many of these are easily degraded and become inactive if kept in a liquid form. Proteins and peptides often exhibit greater stability in the solid state. This results primarily from two factors. First, the concentration of water, a reactant in several protein degradation pathways, is reduced. See Stability of Protein Pharmaceuticals, M. C. Manning, K. Patel, and R. T. Borchardt, Pharm. Res. 6, 903-918 (1989), the complete disclosure of which is herein incorporated by reference. Second, the proteins and other excipients are immobilized in the solid state. Water is a reactant in hydrolysis reactions, including peptide change and cleavage, and deamidation. Reducing the water concentration by freeze-drying or spray drying, reduces this reactant concentration and therefore the rates of these degradation pathways.
The mobility of the peptides or proteins, as well as other molecules in the formulation, are reduced in the solid or dry state. See Molecular Mobility of Amorphous Pharmaceutical Solids Below Their Glass Transition Temperatures, B. C. Hancock, S. L. Shamblin, and G. Zografi, Pharm. Res. 12, 799-806 (1995), the complete disclosure of which is herein incorporated by reference. For the peptides or proteins, this reduces the rate of intermolecular interactions as well as intramolecular conformational changes or fluctuations in conformation. Minimization of intermolecular interactions will reduce protein and peptide aggregation/precipitation, and will also reduce the rate of diffusion of chemical reactants to the protein or peptide which will slow the rate of chemical degradation pathways. Reduction in intramolecular conformational changes reduces the rate at which potentially reactive groups become available for chemical or intermolecular interaction. The rate of this reaction may decrease as the water concentration, and mobility of the protein, is reduced.
One way to produce protein in solid or dry state is to transform the liquid into a fine powder. When used for inhalation delivery, such powders should be composed of small particles with a mean mass diameter of 1 to 5 microns, with a tight particle size distribution. However, this requirement increases the processing and packaging cost of the dry powder. See also U.S. Pat. No. 5,654,007 entitled "Methods and System for Processing Dispersible Fine Powders" and U.S. Pat. No. 5,458,135 entitled "Methods and Devices for Delivering Aerosolized Medicaments", the disclosures of which are incorporated herein by reference.
An easier way to transform a liquid solution to solid or dry form is to use a freeze drying process where a liquid solution is converted to a solid substance that can be readily reconstituted to a liquid solution by dissolving it with a liquid, such as water. Hence, one object of the present invention is to provide a way to store a solid substance and combine the solid substance the with a liquid to form a solution. Once the solution is formed, it is another object of the invention to rapidly transport the solution to an atomization device to allow the solution to be aerosolized for administration. In this way, the solution is aerosolized immediately after its reconstitution so that the degradation rate of the substance is reduced.
A variety of nebulization devices are available for atomizing liquid solutions. For example, one exemplary atomization apparatus is described in U.S. Pat. No. 5,164,740, issued to Ivri ("the '740 patent"), the complete disclosure of which is herein incorporated by reference. The '740 patent describes an apparatus which comprises an ultrasonic transducer and an aperture plate attached to the transducer. The aperture plate includes tapered apertures which are employed to produce small liquid droplets. The transducer vibrates the plate at relatively high frequencies so that when the liquid is placed in contact with the rear surface of the aperture plate and the plate is vibrated, liquid droplets will be ejected through the apertures. The apparatus described in the '740 patent has been instrumental in producing small liquid droplets without the need for placing a fluidic chamber in contact with the aperture plate, as in previously proposed designs. Instead, small volumes of liquid can be placed on the rear surface of the aperture plate and held to the rear surface by surface tension forces.
A modification of the '740 apparatus is described in U.S. Pat. Nos. 5,586,550 ("the '550 patent") and 5,758,637 ("the '637 patent"), the complete disclosures of which are herein incorporated by reference. These two references describe a liquid droplet generator which is particularly useful in producing a high flow of droplets in a narrow size distribution. As described in the '550 patent, the use of a non-planar aperture plate is advantageous in allowing more of the apertures to eject liquid droplets. Furthermore, the liquid droplets may be formed within the range from about 1 .mu.m to about 5 .mu.m so that the apparatus will be useful for delivering drugs to the lungs.
Hence, it is a further objective of the invention to provide devices and methods to facilitate the transfer of liquid solutions (preferably those which have just been reconstituted) to such aerosolizing apparatus so that the solution may be atomized for inhalation. In so doing, one important consideration that should be addressed is the delivery of the proper dosage. Hence, it is still another object of the invention to ensure that the proper amount of liquid medicament is transferred to an aerosol generator so that a proper dosage may be delivered to the lungs.